A gas turbine engine generally includes a fan and a core arranged in flow communication with one another. Additionally, the core of the gas turbine engine generally includes, in serial flow order, a compressor section, a combustion section, a turbine section, and an exhaust section. In operation, air is provided from the fan to an inlet of the compressor section where one or more axial compressors progressively compress the air until it reaches the combustion section, which includes a combustor defining a combustion chamber. Fuel is mixed with the compressed air and burned within the combustion chamber to provide combustion gases. The combustion gases are routed from the combustion section to the turbine section. The flow of combustion gases through the turbine section drives the turbine section and is then routed through the exhaust section, e.g., to atmosphere.
The combustion section generally includes an annular inner liner, an annular outer liner radially spaced from the inner liner, and a combustor dome coupled to upstream or forward ends of the inner and outer liners. A fuel injector or nozzle extends through the dome and is configured to provide a fuel/air mixture to a combustion chamber that is defined between the inner and outer liners. An outer casing or combustor casing circumferentially surrounds the outer liner and at least partially defines an outer plenum or passage between the combustor casing and the outer liner.
The combustion section further includes an ignition system having one or more igniter assemblies mounted or coupled to the outer casing. An igniter portion of the igniter assembly extends generally radially through the outer casing and the outer plenum. An ignition tip portion of the igniter extends at least partially through an opening defined within the outer liner, and a ferrule or other seal member extends around the igniter adjacent the openings to provide a seal against fluid leakage through the opening. During operation of the gas turbine, such as during light-off or restart, the igniter may be energized to provide a spark at the ignition tip so as to ignite the fuel/air mixture within the combustion chamber.
More commonly, non-traditional high temperature materials, such as ceramic matrix composite (CMC) materials, are being used in gas turbine applications. Components fabricated from such materials have a higher temperature capability compared with typical components, e.g., metal components, which may allow improved component performance and/or increased engine temperatures. Accordingly, using a CMC material for the inner and outer liners of the combustor may improve the durability of the liners, as well as allow reduction of impingement cooling or other types of cooling of the liners and increased combustion temperatures, which may improve engine performance. However, CMC materials typically have much lower coefficients of thermal expansion than, e.g., metals or metal alloys, such that CMC components have much lower thermal growth rates than metal components.
Thus, for CMC combustor liners, radial and/or axial positioning of the igniter assembly with respect to the outer liner and/or the combustion chamber may change during operation of the gas turbine. For example, varying thermal growth rates of the outer casing and the CMC outer liner may cause shifting of the position of the seal member adjacent the liner opening, which may result in undesirable fluid leakage through the opening, e.g., from a relatively cold side of the liner to the relatively hot combustion chamber. Consequently, an improved ignition assembly for a gas turbine engine, as well as an improved sealing system for an ignition assembly, would be useful in the turbofan engine industry.